Features of endogenous cardiomyocyte chromatin revealed by super-resolution STED microscopy.

Despite the extensive knowledge of the functional unit of chromatin-the nucleosome-for which structural information exists at the atomic level, little is known about the endogenous structure of eukaryotic genomes. Chromosomal capture techniques and genome-wide chromatin immunoprecipitation and next generation sequencing have provided complementary insight into global features of chromatin structure, but these methods do not directly measure structural features of the genome in situ. This lack of insight is particularly troublesome in terminally differentiated cells which must reorganize their genomes for large scale gene expression changes in the absence of cell division.

Quantitative analysis of the chromatin proteome in disease reveals remodeling principles and identifies high mobility group protein B2 as a regulator of hypertrophic growth.

A fundamental question in biology is how genome-wide changes in gene expression are enacted in response to a finite stimulus. Recent studies have mapped changes in nucleosome localization, determined the binding preferences for individual transcription factors, and shown that the genome adopts a nonrandom structure in vivo. What remains unclear is how global changes in the proteins bound to DNA alter chromatin structure and gene expression.

Specialized compartments of cardiac nuclei exhibit distinct proteomic anatomy.

As host to the genome, the nucleus plays a critical role as modulator of cellular phenotype. To understand the totality of proteins that regulate this organelle, we used proteomics to characterize the components of the cardiac nucleus. Following purification, cardiac nuclei were fractionated into biologically relevant fractions including acid-soluble proteins, chromatin-bound molecules and nucleoplasmic proteins.

Stress signaling by Tec tyrosine kinase in the ischemic myocardium.

Nonreceptor tyrosine kinases have an increasingly appreciated role in cardiac injury and protection. To investigate novel tasks for members of the Tec family of nonreceptor tyrosine kinases in cardiac phenotype, we examined the behavior of the Tec isoform in myocardial ischemic injury. Ischemia-reperfusion, but not cardiac protective agents, induced altered intracellular localization of Tec, highlighting distinct actions of this protein compared with other isoforms, such as Bmx, in the same model.

Post-translational regulation of calsarcin-1 during pressure overload-induced cardiac hypertrophy.

Chronic pressure overload to the heart leads to cardiac hypertrophy and failure through processes that involve reorganization of subcellular compartments and alteration of established signaling mechanisms. To identify proteins contributing to this process, we examined changes in nuclear-associated myofilament proteins as the murine heart undergoes progressive hypertrophy following pressure overload. Calsarcin-1, a negative regulator of calcineurin signaling in the heart, was found to be enriched in cardiac nuclei and displays increased abundance following pressure overload through a mechanism that is decoupled from transcriptional regulation.

Loss of Bmx nonreceptor tyrosine kinase prevents pressure overload-induced cardiac hypertrophy.

Bmx nonreceptor tyrosine kinase has an established role in endothelial and lymphocyte signaling; however, its role in the heart is unknown. To determine whether Bmx participates in cardiac growth, we subjected mice deficient in the molecule (Bmx knockout mice) to transverse aortic constriction (TAC). In comparison with wild-type mice, which progressively developed massive hypertrophy following TAC, Bmx knockout mice were resistant to TAC-induced cardiac growth at the organ and cell level.